In the computer field, particularly in the microprocessor field where circuits are developed as a portion of an integrated circuit, it has heretofore been necessary to employ a large number of devices, which consumes excessive space on the chip, in order to detect an input level to a logic circuit which is greater than normal. Thus, the subject invention relates to a circuit used as a mode switch for a test condition which is simplified, conserves space on the chip, and is accordingly much more reliable.